I'e unsoldered the optocoupler, placed into a breadboard, and used 270ohm resistor (because I've run out of 330) resistors on the 5v side, I was surprise because it runs cool.

What I'am missing here, does the temperature diference is because of saturation of the photo transistor? should I increase the amount of current being transmited into the optocoupler to get it cooler, ou decrease the photo transistor current ?